Hi, I noted that if I associate a page with Gecko, say, then associate the same URL with Trident, then the record of the association with Gecko remains present.
Further, when I finaly found where to modify these records, because I'd tried this a few times, not getting the result I wanted 'cos the record wasn't deleted when the associated engine was changed, I found two entries for the same URL under 'Trident pages' and three under 'Gecko Pages'.
Hope the appropriate software support (together I'd suggest with a prompt such as 'Changing association from Trident to Gecko. Ok?') can be added..